Lock nut



A. R. BREED Nov. 26, 1968 LOCK NUT Filed Feb. 16, 1966 INVENTOR. 5 ART/ UR R. BREED BY A 7') 061V! Y6 United States Patent 3,412,773 LOCK NUT Arthur R. Breed, Euclid, Ohio, assignor to The Lamson & Sessions C0., Cleveland, Ohio, a corporation of Ohio Filed Feb. 16, 1966, Ser. No. 527,965 11 Claims. (Cl. 151-22) ABSTRACT OF THE DISCLOSURE A locking thread convolution for a thread having a theoretical basic thread form. The locking thread convolution has a thread angle and pitch which is the same as that for a standard thread of the same basic thread form and a metal flank thickness which is wider than the maximum metal flank thickness of a standard thread of the basic thread form to provide for uniform thread interference along the flanks of the locking thread convolution when the latter is applied to a mating standard thread. The locking thread convolution also has a recess space between adjacent threads thereof which is larger in an axial plane than that defined by the triangle between adjacent threads of the locking thread convolution to freely accommodate metal swaged due to the thread flank interference. The locking thread convolution is preferably embodied in a lock nut and formed so as to provide a continuation of a plurality of free running threads in the lock nut.

The present invention relates to a locking thread convolution for a thread and in particular to a lock nut having such a locking thread convolution therein which interferes with a mating external thread on a stern when applied thereto. The present invention also relates to a method of making a lock nut.

The present invention provides a new and improved locking thread convolution for a thread having a theoretical basic form, the locking thread convolution having a thread angle which is the same as that for the basic thread form and a metal flank thickness which is wider than that for the basic thread form to provide for uniform thread interference along the flanks of the locking thread convolution when the latter is applied to a mating standard thread and having a recess space between adjacent threads thereof which is larger in an axial plane than that defined by the triangle between adjacent threads of the locking thread convolution to freely accommodate metal swaged due to the thread interference so that seizure between the locking thread convolution and the mating thread does not occur.

The present invention further provides a new and improved locking thread convolution of the character described and in which the recess space between adjacent threads of the locking thread convolution is larger than that defined by the fundamental triangle of the basic thread form, and wherein the recess space preferably extends to a depth greater than the maximum depth for the standard thread of the same basic thread form and preferably deeper than the sharp root of the basic thread form.

The present invention additionally provides a new and improved locking thread convolution of the character referred to and in which the recess has a generally radially extending wall means which is angularly related to the flanks of the thread and preferably intersects the flank of the thread convolution at a location intermediate the crest and bottom of the mating standard thread.

The invention also provides a locking thread convolution which provides a high locking power when applied to a mating standard thread, is not particularly sensitive ice to tolerance variations, and develops the high locking power with little or no tendency to jam or seize.

The present invention also provides a new and improved lock nut having a plurality of thread convolutions along a portion of its length for freely engaging a threaded stern having a standard thread thereon and locking thread convolutions at its trailing end which interfere with the thread on the stem to produce a locking, action, the locking thread convolutions having a recess space between adjacent thread convolutions thereof which is greater in an axial plane that that defined by the triangle between adjacent convolutions and which preferably extends to a depth which is greater than the maximum major diameters for the standard nut thread for freely mating with the threads on the stem for freely accommodating metal swage by the interfering threads so that seizure between the nut and the stem does not occur when the nut is applied thereon.

The present invention additionally provides a new and improved lock nut wherein the locking thread convolutions have the same thread angle as the theoretical basic form for the thread convolutions and a flank width which is wider than that of the basic thread form to provide uniform interference along the flanks thereof when applied to a threaded stem and wherein the recess space between adjacent locking thread convolutions in an axial plane is preferably greater than the fundamental triangle of the basic thread form and preferably extends deeper than the sharp root of the basic thread form.

The present invention further provides a new and improved lock nut, as defined in the preceding paragraphs, and wherein the locking thread convolutions are formed within a radially resilient portion, preferably a collar portion, of the nut which is radially expanded outwardly due to the thread interference and which exerts a self-contracting force due to the radial expansion thereof to effect a further locking action.

The present invention also provides a new and improved method for making a lock nut of the character described from a nut blank having an axially extending opening therethrough 'by first tapping the opening to form a locking screw thread convolution on its side wall which has wider flanks than a standard thread screw convolution of the same theoretical basic form and a recess space between adjacent threads located outwardly of the theoretical basic form for the thread which is larger in an axial plane than the maximum recess space located outwardly from the basic thread form for the standard thread, and further tapping the locking screw thread convolution along a portion of the length of the opening to remove metal from the side flanks thereof to reduce the width therebetween to that of the standard thread along said portion while leaving the remaining portion of the locking thread convolution intact.

Other objects, novel characteristics and advantages of this invention will be apparent in the following detailed description and in the accompanying drawings forming a part of this specification, and in which similar reference numerals designate corresponding parts throughout the several views of the drawings, and in which:

FIG. 1 is an end elevational view of a lock nut embodying the present invention and showing the nut as viewed from the locking end thereof;

FIG. 2 is a side elevational view of the nut showing the same in partial axial section, the view being taken as indicated by the section line 22 of FIG. 1;

FIG. 3 is a side elevational view of the nut showing the same in partial axial section and applied to a threaded stem;

FIG. 4 is an enlarged fragmentary sectional view showing the engagement between the threads on the stem and the locking end of the nut; and

FIG. 5 is an enlarged fragmentary axial sectional view of a cutting tap for making the lock nut.

The present invention provides a novel locking thread convolution which deviates from the theoretical basic form of the thread in a particular manner to provide an improved locking action. The locking thread convolution will provide a high locking power, is not particularly sensitive to tolerance variations and develops the high locking power with little or no tendency to jam. The locking action is obtained by making the threads of the convolution wider than the basic thread form to provide a uniform interference along the flanks thereof when applied to a standard mating thread and by providing a recess space between adjacent threads of the thread convolution which is larger in an axial plane than the recess space defined by the triangle between the adjacent threads thereof to freely accommodate metal swaged by the interfering threads. In the preferred and illustrated embodiment, the recess space is larger than the fundamental triangle of the basic thread form and preferably extends deeper than the sharp root of the basic thread form, and preferably has sides which extend generally radially of the axis of the locking thread convolution and preferably intersecting the flanks thereof at a location intermediate the basic major and minor diameters of the basic thread form.

The basic theoretical design or form of a thread con volution generally provides for a truncation of the fundamental triangle for the thread convolution to provide a flat between adjacent threads at the base of the threads. This flat lies along the surface of an imaginary cylinder coaxial with the thread convolution. For example, in the basic thread design for the screw threads set forth in the National Bureau of Standards Handbook H28 (1957) entitled Screw Thread Standards for Federal Services, published by the U.S. Dept. of Commerce, the basic length of the fiat between adjacent threads in an axial plane of an internal thread convolution is given by the formula 1/ SP, where P is the pitch of the thread. In accordance with established standards for an internal thread convolution, the truncations of the fundamental triangle may occur from a maximum in which the base lenght of flat is 1/ 8P to a minimum such that the base length of the flat is 1/24P. The flat between adjacent threads in an axial plane will lie along what is referred to as the major diameter in an internal thread convolution with the maximum major diameter permitted by the established standards occurring when the base length of the flat is 1/24P.

In accordance with the preferred embodiment of the present invention, the basic thread angle of the thread convolution is maintained, the thread angle being the angle defined in an axial plane by the converging sides of flanks of the thread convolution, but the width of the thread convolution is uniformly wider than that for the basic thread design so as to provide a uniform depth of interference along the flanks of the thread convolution with the standard mating thread. The recess space between the adjacent threads of the thread convolution is preferably larger in an axial plane than the space defined by the fundamental triangle of the basic thread and preferably has a side wall means which extends generally radially of the axis of the locking thread convolution and which intersects the flank of the thread at a radial location which is intermediate the crest and bottom of the standard mating thread when applied thereto and preferably extends to a depth which is greater than the maximum depth permitted between the crest and bottom or root for a standard thread of the same basic thread form. This construction enables a high locking interference to be effected and the extent of the locking interference to be readily controlled and enables a high locking power to be effected with little or no tendency to jam or seize.

Although the novel locking thread convolution of the present invention could be used in various members or fasteners to provide a locking action with a cooperating or mating threaded member, it is particularly useful in a nut to provide a lock nut, and is herein shown as embodied in a lock nut. The lock nut is usable in conjunction with fastening elements having threaded stems, such as bolts or screws, provided with standard screw thread convolutions, such as the screw thread standards set forth in the aforementioned National Bureau of Standards Handbook H28.

As representing a preferred embodiment of the present invention FIGS. 1 and 2 of the drawings show a lock nut 10 comprising a metal body 12 having an opening 14 extending axially therethrough and provided with a screw thread 16 on the side wall 18 of the opening 14. At one end thereof the body 12 has an annular bearing surface 20 in surrounding relation to the opening 14. The nut body 12 is preferably provided at the other end thereof with a radially and circumferentially resilient portion or section which is here shown as being in the form of a collar portion or crown 22 having a reduced transverse dimension. The opening .14 extends entirely through the lock nut 10 including the collar portion 22 thereof.

The screw thread 16 formed on the side wall 18 of the opening 14 comprises a plurality of fully formed, free running screw thread convolutions 16a which are adapted to freely run on or engage the conventional standard thread convolutions on a threaded stem 24 and a plurality of undistorted, nonstandard locking thread convolutions 16b which are adapted to interfere with the standard threads on the stem 24 to produce a locking action therebetween. The thread convolutions 16a define a continuous free running thread or thread convolution which extends from or adjacent the end 20 along the opening 14 for the major portion of the length thereof and terminates adjacent the collar portion 22. The thread convolutions 16:: are standard thread convolutions of the theoretical basic form so as to have a free running engagement with the standard thread on the stem 24, except that they are here shown as having a major diameter which is greater than the maximum major diameter for the standard thread convolutions to facilitate manufacture of the nut 10. Also, tests have indicated that the provision of a major diameter which is greater than the maximum major diameter for a standard thread gives an improved fatigue life for the mating external thread.

The screw thread convolutions 161) form a continuation or extension of the thread convolutions 16a and define a continuous interfering locking thread or thread convolution which extends along the remaining portion of the side wall 18 of the opening 14 and preferably for the full length of the collar portion 22. The locking thread convolutions 16b deviate from the standard thread convolutions of the theoretical basic form for the thread convolutions in that they have a pitch diameter, as indicated by the phantom line 25, which is less than the minimum pitch diameter of the standard thread convolutions of the basic form or the thread convolutions 16a, as indicated by the phantom line 26, and preferably have a major diameter which is greater than the maximum major diameter for the standard thread convolutions of the basic form, the latter major diameter being indicated by the dotted line 28. The thread convolutions 16b are here shown as having planar leading and trailing side flanks 30 and 31, respectively, which have the same flank angle as the leading and trailing side flanks of the thread convolutions 16a and which have an axially extending width at any given radial location which is greater than the corresponding maximum width within established tolerance limits of the standard thread convolution of the basic form or the thread convolutions 16a, as indicated by the dotted lines 32 on the thread convolutions 160. When flank angle is used in the present specification, it refers to the angle that the line of intersection of the flank with a plane through the nut axis defines with the nut axis. The screw thread convolutions 16a and 16b, in the pre ferred embodiment, have a standard crest diameter.

The locking screw thread convolutions 16b of the screw thread 16 define a continuous interfering locking thread portion on the nut which interferes with the threaded stem 24 to produce a locking action therebetween and effects a swaging of metal when the nut is screwed onto the stem 24. Since the screw thread convolutions 16b have a pitch diameter which is less than the minimum pitch diameter of the standard screw thread convolutions, the width of the grooves between adjacent thread convolutions 16b thereof is less than the width between the side flanks of the standard screw thread convolutions on the stem 24. Therefore, when the standard thread convolution on the stem 24 engage the thread convolutions 1612 on the nut 10 they interfere with each other, as indicated in FIG. 4 by the double cross-hatched areas, and cause metal to be swaged. Since the flank angle for the locking thread convolutions 16b is the same as for the standard thread on the stem 24, the locking threads have a uniform depth of interference along the thread flanks.

If the lock nut 10 is of a softer material than that of the threaded stem, the major portion of the metal which is swaged due to the thread interference will be swaged from the thread convolutions 16b of the nut 10 and flow into cavities or recesses 35 extending radially inwardly from the bottom of the thread convolutions 16b. The recesses 35 are larger in an axial plane than the recess space defined by the triangle between the adjacent threads 16b, i.e., the triangle whose sides are coplanar with the flanks and 31 and whose apex is the projected point of intersection of the flanks, as indicated by reference numeral 36. The recesses 35, in the preferred embodiment, extend radially outwardly to a depth which is greater than the depth defined by the maximum major diameter for the standard thread of the same basic thread form and preferably to a depth greater than the sharp root of the basic thread form, the sharp root being indicated by reference numeral 40. The recesses 35 preferably have opposite side wall portions 42 which extend generally radially outwardly of the axis of the nut and which intersect the interfering flanks of the threads 16b preferably at a location radially inwardly of the basic major diameter of the basic thread form or radially inwardly of the crest of the standard thread on the stem 24, as best shown in FIG. 4. It is thus apparent that each of the recesses 35 includes a clearance space or recess portion extending outwardly from the basic thread form which is substantially larger in an axial plane than the maximum clearance space extending outwardly from the basic thread form for the standard thread within established tolerances so that the metal swaged is freely accommodated or received in the recesses 35 to insure that seizure between the nut .10 and the stem 24 due to insufiicient clearance space for the swaged metal will not occur. By providing generally radially extending sides 42 for the recesses 35 which preferably intersect the flanks of the thread convolutions 16b at a location radially inwardly of the crests of the threads on the stem 24, metal is swaged from the flanks of the thread convolutions 16b along their entire extent so that a maximum locking action is achieved. This latter provision also insures that free access to the recesses 35 is provided for the swaged metal.

If the nut 10 is of a harder material than the threaded stem 24 metal will be swaged from the threads of the stem 24 into the cavities 35 and into the normal clearance space provided between the crests of the threads 16b of the nut and the root or bottom of the threads on the stem, this latter clearance space being usually suflicient to freely accommodate that portion of the metal which is swaged thereinto due to the thread interference. If additional clearance space between the crests of the threads 16b of the nut and the root of the threads on the stem is necessary or desired, such as may be necessary in extreme hard-soft material combination, the crest diameter of the threads 16b can be made greater than the maximum crest diameter for the standard thread to provide extra clearance space between the crests of the threads 16b and the root of the threads on the stem.

A locking action between the threads 16b and the threads on the stem 24 is also produced, in the preferred embodiment, by the self-contracting forces exerted by the collar portion 22 due to the latter being expanded circumferentially and radially outwardly as a result of the thread interference therein. That is, the collar portion 22 due to its resilient or flexible nature will tend to return to the position which it had prior to being expanded radially outwardly by the threads of the stem 24 and thus, will exert a self-contracting or radially inward force on the threads on the stem 24. By forming the locking thread convolutions 16b in the radially resilient collar portion 22 of the nut 10, a locking portion on the nut 10 is provided which is of a sufficient flexibility to accommodate the tolerance variations of the standard threads on the stem 24 and the threads 16b in the locking portion of the nut 10.

From the construction of the preferred embodiment lock nut 10 as shown in FIGS. 1 and 2 in the drawings and described above, it can be seen that the thread convolutions 16a provide for free running engagement with the threads of the stem 24 and that gripping of the threaded stern by the nut 10 for producing a desired locking action is achieved, first, by the thread flank in terference between the threads of the stem 24 and the locking threads 1612 in the collar portion 22. A locking action is also achieved, as explained above, by the selfcontracting flexibility of the collar portion 22 by which the screw threads 1612 are pressed against the threads on the threaded stem 24. The locking action achieved between the nut 10 and the threaded stem 24 will accordingly be very effective for preventing undesired loosening between the nut 10 and the stem 24. The provision of the cavities 35 permits a thread interference type locking action to be achieved without causing seizure between the nut 10 and the stem 24 and will permit unscrewing therebetween as well as the reapplication thereof in which a locking action is again achieved to a substantial degree due to the self-contracting flexibility of the collar portion 22.

The collar portion 22 is here shown as comprising an annular side wall 44 having a radial wall thickness which is substantially less than the radial wall thickness of the side wall of the nut body 12. The collar portion 22 defines a closed wall means which encompasses or completely surrounds the opening 14 and which is integral with the nut body 12 for the entire circumferential and a transverse extent of the annular side wall 44.

If a collar portion having a greater radial resiliency than the collar portion 22 were desired, the collar portion 22 could be provided with a pair or pairs of grooves at diametrical opposite locations therein. The grooves would extend axially of the collar portion for the entire length thereof and preferably extend through the side wall of the collar portion. The grooves would open into the opening and be of a sufficient width between their adjacent side wall portions thereof so that their axially exending corner edges 'formed at the junction with the opening 14 in the nut would not act as cutters when the nut is applied to the threaded stem 24. The provision of grooves would also provide additional recess means for receiving metal swaged due to the thread interference between the locking threads in the collar portion and threads on the stem 24.

The lock nut 10 can be suitably formed as by a cold working operation on a metal blank in a suitable die apparatus whereby a nut blank having a central opening and a desired external shape, such as a hexagonal shape shown in the drawings, is provided and wherein the external shape formed by the die apparatus includes the collar portion 22. The die apparatus used for thus forming the nut blank is of such a character that the formed shape of the collar portion 22 on the nut body 12 is of a reduced transverse dimension as referred to above.

After the nut blank is so formed, the screw thread 16 is formed on the side wall 18 of the opening 14 by a tapping operation. The screw thread 16 can be formed by an in and out operation of a cutting tap 50 having a forward section 51 provided with culting teeth which are undercut along their flanks, as indicated by reference numeral 52 and which preferably have a. crest diameter which is substantially greater than the maximum allowable for cutting the standard thread and a rearward sec tion 53, here shown as being axially spaced from the forward section, provided with cutting teeth for cutting a standard thread. As the forward section of the cutting tap moves into the opening 14 from the bearing end 20, it cuts threads on the side wall of the nut blank like the thread convolutions 16b and when the rearward end of the cutting tap moves into the opening 14 it removes the excess metal left on the flanks of the thread convolutions 16]) because of the undercut flanks of the cutting teeth at the forward end of the tap to provide thread convolutions like the thread convolutions 16a. The cutting tap is moved into the opening 14 until the forward end of the rearward section is located at approximately the start of the collar portion 22 of the nut and then backed out, thus leaving the thread convolutions 16b cut by the forward section of the tap in the collar portion 22 intact. The cutting teeth at the forward ends of the forward and rearward sections 51 and 53, respectively, are preferably charnfered or tapered with the cutting teeth at the forward end of the rearward section 53 providing a smoo;h or gradual transition between the cross-sectional shape of the cutting teeth of the two sections.

From the accompanying drawings and the foregoing detailed description, it will now be readily recognized that this invention provides a novel locking thread convolution which deviates from the theoretical basic form of the thread in a particular manner to provide an improved interference-type locking action when applied to a mating threaded member without causing seizure between the interfering threads thereof. It will also be seen that the present invention provides a novel lock nut which is of a simple and economical construction and which provides a thread interference-type locking action without causing seizure between the nut and a threaded stem. It will additionally be recognized that a novel lock nut has been provided in which the thread flank interference takes place within a collar portion of reduced transverse dimension so that an additional locking action due to the radial expansion of the collar is effected and that due to the flexible nature of the collar portion further assurance against seizure between the threads on the nut and the threads on the stem is provided.

Although the subject matter of this invention has been illustrated and described herein to a somewhat detailed extent, it will be understood, of course, that the invention is not to be regarded as being limited correspondingly in scope but includes all changes and modifications coming within the terms of the claims hereof.

Having described my invention, I claim:

1. A locking thread convolution for a thread having a theoretical basic form and standard tolerances from the basic form and which is adapted to interfere with a standard mating thread to provide a locking action therebetween, the locking thread convolution having a thread angle which is the same as that for the basic thread form and a metal width between its flanks which is greater than the maximum width for a standard thread of the same basic thread form to provide for uniform interference with a standard mating thread substantially along the flanks of the locking thread convolution, said locking thread convolution having a pitch between adjacent threads thereof which is the same as that for a standard thread of the same theoretical basic thread form, said locking thread convolution having a recess space between adjacent threads thereof for freely accommodating metal swaged due to the thread interference, said recess having side wall portions extending transversely to the longitudinal axis of said locking thread convolution and which intersect the adjacent flanks of the thread at locations intermediate the crest and bottom of the mating standard thread and a bottom which is radially spaced from the crest of the mating standard thread to provide clearance between the crest of the standard mating thread and the bottom of said locking thread convolution, said locking thread convolution having a crest radially spaced from the root of the standard mating thread to provide clearance between the crest of the locking thread convolution and the root of the standard mating thread.

2. A locking thread convolution, as defined in claim 1, wherein said recess space extends radially to a depth greater than the sharp root for the basic thread form.

3. A lock nut for cooperating with standard screw thread convolutions on an externally threaded stern comprising; a metal nut body having an axially extending opening therethrough, a screw thread formed on the side wall of said opening comprising first screw thread convolutions having a given pitch diameter extending inwardly from the end of said opening and terminating at a location spaced axially inwardly from the other end of the opening and which are adapted to freely engage the standard screw thread convolutions on said stem, and second locking screw thread convolutions which are adapted to interfere with the threads on said stem and effect a swaging of metal when the nut is threaded onto the stem, said second thread convolutions forming an extension of said first screw thread convolutions and extending from said location toward the other end of said opening, said second screw thread convolutions being truncated and having the same pitch and thread angle as standard screw thread convolutions of the same theoretical basic thread form, said second screw thread convolutions having a minor diameter no less than the minor diameter of standard screw thread convolutions of the same theoretical basic thread form, said second screw thread convolutions deviating from standard screw thread convolutions of the same theoretical basic thread form in that they have a width between their flanks in an axial plane which is greater than the maximum width for the standard thread convolutions and a recess space between adjacent convolutions thereof for freely accommodating metal swaged due to the thread interference, said recess between adjacent locking thread convolutions having a side wall portion extending transversely to the longitudinal axis of said lock nut and angularly related to the flanks thereof and intersecting one of the flanks at a location intermediate the crest and root of the standard thread convolutions on the stern and a bottom which is located radially outwardly of the maximum major diameter of the standard screw thread convolutions on said stem to provide clearance between the crests of the threads on said stem and the bottoms of the second locking thread convolutions.

4. A lock nut, as defined in claim 3, and wherein said recess space between adjacent locking thread convolutions extends radially outwardly to a depth greater than the sharp root for the basic thread form for the thread convolution.

5. A lock nut, as defined in claim 3, wherein said recess also has a radially extending side wall portion which intersects the other of the flanks of the second thread convolutions.

6. A lock nut, as defined in claim 3, wherein said nut body has a radially resilient portion at one end and wherein said second locking screw thread convolutions are located in said radially resilient portion, said radially resilient portion expanding radially due to the thread interf-erence and exerting a self-contracting force when radially expanded to further increase the locking action between the interfering thread convolutions.

7. A lock nut, as defined in claim 6 wherein said radially resilient portion comprises an annular collar having a side wall thickness which is substantially less than the side Wall thickness of the nut body.

8. A lock nut, as defined in claim 7, wherein said collar portion comprises a closed wall means encompassing said opening, said closed wall means being integral with said nut body for the entire circumferential and transverse extent of said closed wall means.

9. A lock nut for cooperating with standard screw thread convolutions on an externally threaded stem comprising a metal nut body having an axially extending opening therethrough, a screw thread formed on the side wall of said opening comprising first screw thread convolutions having a given pitch diameter extending inwardly from one end of said opening and terminating at a location spaced axially inwardly from the other end of the opening and which are adapted to freely engage the standard thread convolution on said stem, and second locking thread convolutions forming an extension of said first screw thread convolutions and extending from said location to the other end of said opening and which are adapted to interfere with the threads on said stem and effect a swaging of metal when the nut is threaded onto the stern, said second screw thread convolutions having the same flank angle and pitch as said first thread convolutions and a minor diameter no less than the minor diameter of standard screw thread convolutions of the same theoretical basic thread form, said second screw thread convolutions deviating from standard screw thread convolutions of the same theoretical basic thread form in that they have a width between their flanks in an axial plane which is greater than the maximum width for the standard screw thread convolutions to provide a uniform interference with a standard mating thread along the flanks of said second thread convolutions and a recess space between adjacent thread convolutions thereof for freely accommodating metal swaged due to the threaded interference, said recess space between adjacent locking thread convolutions being larger in an axial plane than the space defined by the triangle between the adjacent locking thread convolutions for freely accommodating the metal swaged due to the thread interference, said recess having side portions which intersect the adjacent flanks of said second screw thread convolutions at locations intermediate the crest and bottom of the mating standard thread convolutions and which extend transversely of a 1ongitudinal axis of said lock nut and a bottom which is located radially outwardly of the maximum major diameter of the standard screw thread convolutions on said threaded stem to provide clearance between the crest of the threads on said stem and the bottom of said second locking thread convolutions.

10. A lock nut as defined in claim 9, and wherein said second locking screw thread convolutions have a major diameter which is greater than the maximum major diameter for standard screw thread convolutions for freely engaging the threads on said stem.

11. A locking thread convolution for a thread having a theoretical basic form and standard tolerances from the basic form and which is adapted to interfere with a standard mating thread to provide a locking action, the locking thread convolution having a thread angle which is the same as that for the basic thread form and a metal width between its flanks which is greater than the maximum width for a standard thread of the same basic thread form to provide a uniform interference with a standard mating thread substantially along the flanks of the locking thread convolution, said locking thread convolution having a recess space between adjacent threads thereof which is larger in an axial plane than the space defined by the triangle between adjacent threads of said locking thread convolution, said recess having a side wall portion extending transversely to the longitudinal axis of said locking thread convolution and a bottom which is radially spaced from the crest of the mating standard thread to provide clearance between the crests of the mating standard thread and the bottom of said locking thread convolution, said locking thread convolution having a crest radially spaced from the root of the standard mating thread to provide clearance between the crest of the locking thread convolution and the root of the standard mating thread.

References Cited UNITED STATES PATENTS 2,371,365 3/1945 Tomalis et a1. 151-22 2,437,638 3/1948 Evans 151-22 224,591 2/ 1880 Harvey 151-22 1,369,156 2/1921 Woodward 151--22 2,567,483 9/ 1951 Hotine.

2,741,288 4/1956 Johnson 151-7 3,233,258 2/1966 Neuschotz 15141.73

FOREIGN PATENTS 963,110 7/ 1964 Great Britain.

CARL W. TOMLIN, Primary Examiner. RAMON S. BRITTS, Assistant Examiner. 

